TypeScript enum alternative

Define a list of strings that represents a set of entities, using Literal Types instead of Enum

TypeScript

Let’s start from a list of strings that represent a set of entities, for example the fields of a table:

const myFields = [
  'startDate',
  'endDate',
  'price',
  'quantity',
]

My goal is to have a MyField type equivalent to

type MyField = 'startDate' | 'endDate' | 'price' | 'quantity'

And a Type Guard to check for that type, name it isMyField for instance.

Then the whole implementation will be the following:

export const myFields = [
  'startDate',
  'endDate',
  'price',
  'quantity',
] as const;

export type MyField = typeof myFields[number];

export function isMyField(value: unknown): value is MyField {
  if (typeof value !== 'string') return false;
  return (myFields as readonly string[]).includes(value);
}

If for example I create a field with a wrong value I will get an error:

const myField: Field = 'starDate'
// TS will complain with message like:
// Type 'starDate' is not assignable to 'startDate' | 'endDate' | 'price' | 'quantity'